Tuesday, June 7, 2016

As a side effect of the movers taking most of my furniture, I had to move the LM-1s off their stands 2 feet from the rear wall to half that distance, sitting on books on the TV stand.

In this location I find them too boomy. What's the solution? Socks. I put a big clean fluffy white sock to plug the port in the back of each. Problem solved! They don't sound as good as they did further away, and further apart, but they have regained their tonal composure.

Sunday, June 5, 2016

A number of readers have asked me about the horizontal layout of the drivers. I was just being creative with the pictures, but I personally listen to the LM-1's with the traditional tweeter-over-woofer, "portrait mode" arrangement. Of course, you can lie them down to fit tight spaces, or to keep a lower profile over a mixing console, but I am not intentionally designing "landscape mode" speakers.

The LM-1 has a wide and natural dispersion but is best with the tweeters on the outside and either parallel or toed in. Vertically however the LM-1 sounds best with your ears at tweeter level or lower. Any higher and it sounds dull and lifeless.

The LM-1C is similar. Used vertically keep the tweeters to the outside of center, toed in slightly. Around 15 degrees. This will give you a big sweet spot in the center, and limit reflections to the side. Used horizontally keep the tweeter pointed at or slightly above the tweeter towards the listener location, You may wish to experiment with the tweeter on the "outside" of the TV. In other words, keep the woofers closer to the TV than the tweeter but tilt the speaker vertically. Play around with it a little and the best tuning will become pretty obvious.

The LM-1 speaker kit has only been promoted for a little while and already it's evident there's a lot of misinformation and attempts to discredit the design. I hope it doesn't become the Kardashian (any of them) of speaker kits. In any event, one completely inaccurate criticism is that the frequency response is below-average. Nonsense. Could you use different parts and asymptotically approach perfection? Probably. You could get different, but getting noticeably better will be very difficult.

Let's go over some background.

Who is Bruel and Kjaer?

When scientists and engineers think of high-end acoustical instruments Bruel and Kjaer is among the most respected names there is. One famous bit of knowledge that has come out of that organization is the ideal B&K speaker curve, which I happen to like a lot (that's a personal preference). It is meant to be as the ideal response at the listening position. I copy it here, below:

Note that it is not flat! A speaker that measured flat at the listening location would be an ear drill. The B&K curve is about +3dB at 70 Hz or so and -3dB at 20 kHz. Quasi-anechoic measurements measure the speaker driver in near-field, with the expectation that at a distance the measurement would become like you see here. The full discussion of why this is beyond the scope of this posting, but do your research and you'll find much more written about it. You may also find that the Dirac Live target curves, also follow the B&K model of a gently descending response. The point is, I don't make this stuff up. Flat at the listening location is not actually ideal. What is ideal is open to some interpretation. I'm choosing the B&K curves as a matter of taste.

So, how does the LM-1 do by comparison to this fabled B&K curve in real life? Let's comapre (LM-1 level is offset and measured in a bookshelf):

Damn well! This is the plot with R1 = 4.2 Ohms (2.7 + 1.5 actually). I'm packing and that's all the resistors I have on hand.

So, what does this say? This is an objectively neutral speaker kit. If you are looking for a true bookshelf speaker system with reference grade frequency response the LM-1 will do it for you, within the limits of what a small monitor can do. Also, as discussed, the treble balance is up to the builder. If you don't like it, change it. :) I have a feeling that most listeners will like a value closer to 3.9 Ohms or so.

Saturday, June 4, 2016

My usual go-to medium grade capacitor is Mundorf MKP, but since I had such good results with the Clarity MR caps in my reference speakers I decided to try the Clarity ESA's. 24 hours into the experience and it's still too hard.

I've increased R1 from 2.7 to 4.2 Ohms and it's much better. The LM-1 curves match the center channel curves more closely. However I'm still not quite satisfied with the treble. Of course, this is a $35 ring radiator tweeter, vs. the $500 Mundorf AMT I've gotten used to. The two may never closely align, but I have hopes. I've heard lesser tweeters smooth out with better caps, and I've heard caps mellow out after a few days, so this may take a while before I'm ready to say I'm done.

June 5, 2016
At about 48 hours the caps got noticeably less harsh. It's also interesting to note that changing R1 from 2.7 to 4.2 made only about 1.6 dB of difference at 13 kHz, but it's all the difference in the world to my ears.

June 6, 2016
In spite of the packing going on around here, I closed some drapes and listened more last night. I'm ambivalent over the total treble balance, but the tweeter and C1 seem to have settled in quite nicely. I sometimes feel it may still be a little bright, but the measurements don't lie, I'm actually just under the B&K curve, so I'm going to leave it alone. Honestly I think my reference speakers are a little dark, so this may be a good chance for my own ears to adjust. My PC is getting packed up today, so I'll be unable to do more measurements or design as I won't have access to my only Windows 7 PC. This will be a good chance for me to explore what else is available on Ubuntu/Linux! :)